The invention relates to a cylindrical mount for adjustable optical components.
Mounts of this type are known, for example from U.S. Pat. No. 3,951,522, for photographic lenses in which lens elements can be displaced axially relative to other lens elements for the purpose of focussing or varying the focal length. During the displacement, rotations of the lens elements are generally to be avoided, in order to avoid the latter being affected by any centering errors which may be present.
For this purpose, the lenses have, in a fixed mount part, one or more milled reliefs which run parallel to the cylinder axis and in which there is guided in each case one block fastened on the variator (rectilinear guide). Fastened on the block is a roller which engages in a cam path milled in the cam carrier. During a rotation of the cam carrier, the variator is pushed back and forth along the cylinder axis in accordance with the cam profile.
The variator is designed as a cylinder which, by way of a suitable fit, slides in the fixed cylindrical mount part. The roller, which is guided in the cam carrier, also subjects the variator to a force component in the direction perpendicular to the cylinder axis if sliding resistances occur, this resulting in slight tilting in the cylinder guide. Said tilting is generally absorbed by the sliding properties of the cylinder surfaces and lubricants, but may also result in sluggishness or even jamming. However, tilting of the variator also means tilting of the optical components, retained in said variator, in relation to the optical axis, with the result that the image quality is also thus adversely affected.
The cam paths in the cam carrier and the roller diameter have to be coordinated very precisely with one another in order to ensure zero backlash during reverse movement. It is known from JP 59087414 for the guide path to be formed trapezoidally in a fixed mount part and the roller diameter to be selected such that it can engage in the guide path from the wider side. Zero backlash is achieved by resilient contact pressure against the trapezium flanks. The abovementioned force component in the direction perpendicular to the cylinder axis is thus enhanced and naturally also acts on the roller axis, and this may also result in sluggishness of the roller in the cam path. More serious, however, is the fact that, in the case of a plurality of guide paths, cam paths and transmission elements, assigned thereto, in a mount, product tolerances may result in redundancy of the components which are to be adapted to one another, this then resulting in sluggishness of the cylinder guide.
FR 1 271 653 discloses a mount in which an inner variator is provided, on its outer circumferential surface, with an encircling triangular groove in which three balls which are offset in relation to one another run. The variator is enclosed by a sleeve which, parallel to the optical axis, has three slots which serve as rectilinear guide paths for the balls. The sleeve is mounted rotatably on a cam carrier which is fixed relative to the mount, the balls running in cam paths which are made in the inner surface of the cam carrier. The variator is supported on the cam carrier merely via the balls and is guided and centered thereby. During a rotation of the sleeve, the variator is displaced along the optical axis of the mount by the balls following, on the one hand, in the groove on the variator, the rotation of the sleeve and, on the other hand, in the rectilinear guide path of the sleeve, the cam path in the cam carrier.
In order to ensure that the sleeve can rotate without obstruction, it is necessary to provide, between the variator and the cam carrier, sufficient space, which can also compensate for dimensional tolerances in the diameter of the balls and the depth of the guide paths. A slight offset of the variator in the direction perpendicular to the optical axis and slight tilting in relation to the optical axis cannot be avoided and can only be kept within tenable limits by high-outlay production with very narrow dimensional tolerances. In the case of sluggishness of individual balls of the variator, rotation of the variator cannot be ruled out.